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How to Add a Column in SQL

Problem:

You want to add a new column to an existing table.

Example:

We would like to add the column color of the datatype varchar to the table called jeans.

Solution 1:

ALTER TABLE jeans
ADD color varchar(100) NOT NULL;

Discussion:

SQL provides the statement ALTER TABLE that allows you to change the structure of a table. It is used to modify the table by adding a new column. Place the ALTER TABLE keyword followed by the name of the table you want to change. The next is the keyword ADD, after which the name of the new column is specified. It is then followed by the definition of the column: the datatype and any additional constraints. After the ADD, you define the column in the same way as when you create a new table (after the CREATE TABLE in parentheses).

In the example above, we modified the structure of the table jeans. The name of the table, jeans follows the ALTER TABLE. We specify the column to be named, color, after the ADD keyword. At the end of the statement, we specify varchar(100) as the datatype for the values that will be stored in the column color, and the constraint NOT NULL because we don’t want to allow empty values in this column. However, if the table has records, first add the new column allowing NULL, update the data, then in the final step change the definition of the column to NOT NULL.

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